1. Field of the Invention
The present invention relates to a display device including a circuit formed with a transistor, and a method for manufacturing the display device.
2. Description of the Related Art
Various metal oxides exist and are used for a variety of applications. Indium oxide is a well-known material as a metal oxide and is used as a light-transmitting conductive material which is necessary for liquid crystal displays and the like.
Some metal oxides have semiconductor characteristics. As metal oxides having semiconductor characteristics, for example, there are tungsten oxide, tin oxide, indium oxide, zinc oxide, and the like, and a transistor in which a channel formation region is formed using such a metal oxide having semiconductor characteristics has been proposed (for example, see Patent Documents 1 to 4 and Non-Patent Document 1).
As metal oxides, multi-component oxides as well as single-component oxides are known. For example, InGaO3(ZnO)m (m is a natural number) having a homologous series is known as a multi-component oxide semiconductor including In, Ga, and Zn (see Non-Patent Documents 2 to 4).
In addition, it has been confirmed that an oxide semiconductor layer including such an In—Ga—Zn-based oxide can be used as a channel layer of a transistor (see Patent Document 5, and Non-Patent Documents 5 and 6).